The present invention relates generally to continuous casting systems wherein molten metal is continuously cast into metal rod, and more particularly, relates to a pouring pot for pouring molten metal into a continuous casting mold at a substantially constant flow rate.
In the continuous casting of metal rod, molten metal is transferred from a melting furnace or holding furnace to a continuous casting mold formed in a rotary mold ring and the mold ring is rotationally driven to effect continuous casting of the molten metal into cast rod. Since the transfer of molten metal occurs while the mold ring is rotating, it is necessary to accurately control the pouring of the molten metal into the casting mold in order to obtain a satisfactory cast rod product.
Prior to the advent of continuous casting systems, it was common practice in the metal foundry field to pour the molten metal directly from the melting furnace into stationary casting molds and sufficiently accurate control of the pouring could be obtained since such was a batch pouring. However, due to the large and cumbersome construction of the melting furnaces and their difficulty in handling, an intermediate pouring pot was introduced at a location between the melting furnace and the casting molds and the pouring pot functioned as a temporary reservoir for the molten metal and enabled more accurate control of the pouring of the molten metal into the casting molds. Since casting with stationary molds is basically a batch process, sufficiently accurate control of the pouring of molten metal from the intermediate pouring pot into the casting molds can be accomplished using comparatively crude manual and mechanical controls.
In continuous casting systems, however, the molten metal is poured into a moving casting mold and therefore much greater accuracy in control of the pouring of the molten metal into the casting mold is required than in conventional metal foundry practice using stationary casting molds. It has thus become common practice in the continuous casting art to employ an intermediate pouring pot to more accurately control the pouring of the molten metal into the continuous casting mold.
The primary function of the pouring pot is to discharge the molten metal directly into a moving casting mold at a substantially constant flow rate so that the molten metal is uniformly fed to the casting mold. The discharge flow rate of the molten metal from the pouring pot is proportional to the discharge velocity of the molten metal which in turn is a direct function of the molten metal pressure head in the pot. Thus, as the amount of molten metal in the pouring pot varies, the pressure head likewise varies causing fluctuations in the discharge flow rate. The molten metal is customarily fed from the melting furnace to the pouring pot at a nonuniform rate and one function of the pouring pot is to compensate for variations in the feeding rate of molten metal from the melting furnace and discharge the molten metal into the moving casting mold at a substantially constant flow rate.
A major difficulty in maintaining a constant discharge flow rate of molten metal from the pouring pot resides in compensating for fluctuations in the molten metal depth which are caused by different rates of charging and discharging of molten metal into and out of the pouring pot. As any change in depth of the molten metal in the pouring pot results in a proportionate change in discharge flow rate, it is necessary to either minimize depth changes and maintain them within controlled limits or accept such changes in molten metal depth and compensate for them. Much emphasis has been placed on the latter type of control and to this end, it is now common practice to employ a metering device for metering the discharge flow rate and adjust for changes in the molten metal depth. The metering device typically comprises an adjustable metering pin which controls the rate of molten metal flow by increasing or decreasing the outlet opening in the pouring pot. The disadvantage of this type of control is that if it is done manually, it requires the constant attention of a workman and if it is done automatically, it requires additional equipment and controls thereby increasing production and maintenance costs. Moreover, it has not been possible to date to design a completely satisfactory automatic system.
The other type control comprises simply increasing the overall volume of the pouring pot so as to reduce the amount of molten metal depth change for a given change in total volume of molten metal in the pouring pot. However, this technique is disadvantageous in that it requires a much larger and more massive pouring pot which, when filled with molten metal, has considerable weight. Hence, a more massive supporting structure is needed to support such a large volume pouring pot and in the case of an accident, such poses a much greater possibility of danger to workmen in the area then would be the case with smaller volume pouring pots. Moreover, should any problem occur requiring draining of the molten from the pouring pot, a large volume pouring pot is more disadvantageous than a small volume one in that it results in a larger amount of wasted material.
Prior art pouring pots generally have a box-like configuration having at the base region thereof sloped bottom walls. A pouring spout is connected to one of the sloped walls so as to pour the molten metal out of the pouring pot at an angle. The pouring pot has a small molten metal surface area so that a given change in the total amount of molten metal in the pouring pot results in a comparatively large change in the molten metal depth causing a proportionate change in the discharge flow rate of molten metal from the pouring pot. Fluctuations of the molten metal depth cause proportionate fluctuations of the discharge flow rate so that the molten metal is fed unevenly to the casting mold. To compensate for variations in the molten metal depth, it is necessary to employ either an automatic metering device which is relatively sophisticated and expensive or a manual metering device which must be continuously adjusted during use.